A heat recoverable article is an article the dimensional configuration of which may be made substantially to change when subjected to heat treatment.
Usually these articles recover, on heating, towards an original shape from which they have previously been deformed but the term "heat-recoverable", as used herein, also includes an article which, on heating, adopts a new configuration, even if it has not been previously deformed.
In their most common form, such articles comprise a heat-shrinkable sleeve made from a polymeric material exhibiting the property of elastic or plastic memory as described, for example, in U.S. Pat. Nos. 2,027,962, 3,086,242 and 3,957,372. As is made clear in, for example, U.S. Pat. No. 2,027,962, the original dimensionally heat-stable form may be a transient form in a continuous process in which, for example, an extruded tube is expanded, whilst hot, to a dimensionally heat-unstable form, but in other applications, a preformed dimensionally heat-stable article is deformed to a dimensionally heat-unstable form in a separate stage.
In the production of heat recoverable articles, the polymeric material may be cross-linked at any stage in the production of the article that will enhance the desired dimensionally recoverability. One manner of producing a heat-recoverable article comprises shaping the polymeric material into the desired heat-stable form, subsequently cross-linking the polymeric material, heating the article to a temperature above the crystalline melting point or, for amorphous materials the softening point, as the case may be, of the polymer, deforming the article and cooling the article whilst in the deformed state so that the deformed state of the article is retained. In use, since the deformed state of the article is heat-unstable, applications of heat will cause the article to assume its original heat-stable shape.
Such articles have been widely used for many years for enclosing objects such as electrical equipment, wiring and the like in order to protect them from the environment and to provide electrical insulation. The articles may be extruded in the form of a tube or may be formed as discrete pieces by moulding operations, and in either case a layer of adhesive may be provided on the interior surface of the article. However the production of moulded articles is a relatively expensive process involving performing operations on individual items which makes the cost of such articles inappropriate for certain applications. It has been proposed, for example in U.K. applications Nos. 2083403 and 2095617 to form discrete articles by welding together parts of tubing that may be rendered heat-recoverable either before or after the welding step. Such welding processes have the disadvantage that it is not possible, or at least very difficult, to provide the articles with an internal layer of adhesive.